The alkoxylation of alcohols can be conducted using various catalysts. For example, a typical method of alkoxylating an alcohol is one employing KOH as a catalyst.
In recent years, the alkoxylation of alcohols has been conducted using alkaline earth metal based catalysts. Such alkaline earth metal based catalysts are disclosed in U.S. Pat. Nos. 4,775,653; 4,835,321; 4,754,075; 4,820,673; 5,220,077; 5,627,121; and U.S. Patent Publication 2007/0060770, all of which are hereby incorporated by reference for all purposes. These alkaline earth metal based catalysts are preferred for alkoxylation reactions, particularly the alkoxylation of alcohols, primarily for their ability to produce what are known as peaked ethoxylates as discussed more fully in the patents and patent applications referenced above. As is well known to those skilled in the art, the peaked ethoxylates impart certain desirable properties for the end use applications such as surfactants, detergents, etc.
In the typical alkoxylation reaction, regardless of the catalyst employed, an alkylene oxide, e.g., ethylene oxide, is reacted with a compound having an active hydrogen atom, e.g., an alcohol. It is to be understood however, that the alkoxylation of other compounds having active hydrogens, such as carboxylated compounds, can also be conducted by this condensation reaction with a suitable alkylene oxide and suitable catalyst.
Typically, the alkylene oxide employed contains from 2 to 4 carbon atoms, more preferably, 2 to 3 carbon atoms. Thus, ethylene oxide and propylene oxide are generally the alkylene oxides chosen in most alkoxylation reactions.
There are several problems posed by alkoxylation reactions, particularly alkoxylation reactions involving alkaline earth metal based catalysts as described in the above listed patents and patent publications. One such problem is the fact that some alkoxylated alcohols are subject to oxidation. Presently, the use of butylated hydroxyl toluene (BHT) as an antioxidant for alkoxylates is added to the final product, i.e., the alkoxylated alcohol, as it is being loaded in to tank cars or other vessels for transportation. The oxidation problem is particularly acute with respect to alcohol alkoxylates containing a high mole content of the alkoxylates. In this regard, such high mole alkoxylates have to be heated to remain liquid and therefore pumpable into tank cars and other containers. The heat needed to maintain the alkoxylates in liquid form further perpetuates their oxidation. Additionally, it is difficult to assure uniform mixing of the antioxidant and the alcohol alkoxylates within the transportation vessel and indeed to a large extent mixing, to the extent it is conducted, is simply a result of the splashing of the liquid in the tank cars, or other transport vessels. It is hoped that this incidental mixing will dissolve the antioxidant before air oxidation can ensue.
Another problem typically encountered during the alkoxylation of alcohols, particularly alcohols having significant vapor pressures at the temperatures of typical alkoxylation reactions, e.g., 150 to 175° C., is reduced head space in the vessel. Because the reaction is conducted in a closed vessel, the high vapor pressure of the alcohols causes the head space pressure of the reactor to be filled with the partial pressure of the alcohol vapor. This alcohol vapor pressure coupled with nitrogen head space pressure, added to the reactor for safety purposes, vastly reduces head space available for the generally gaseous alkylene oxides. The effect is a cascading one since the added alkylene oxide causes the reactor pressure to build up and prevents further addition of alkylene oxide. The result creates difficulty in initiating the reaction and reduces production of the desired alkoxylate.